Jacques-Louis David based his paintings in ancient Rome because he painted in the Neoclassic style of art. The Neoclassicists painted with classical techniques - very linear figures, often highly idealized. Also, the discovery of the ancient cities of Herculaneum and Pompeii (excavations in 1738 and 1748, respectively) renewed interest in the anceint Roman stories (David lived from 1748-1825). As the French revolution began, many Neoclassic painters would depict scenes of ancient Roman stories that they felt matched the ideals of the current situation - the binding together nature of Roman patriotism (seen in such works as the Oath of the Horatii) - was similar to the ideals of the current French revolution - working together to create reform and revolution. David was actually at the forefront of the revolution - he was a member of the Jacobins, a group of revolutionary extremists. He was also close with Marat, another Jacobin who was assassinated, and painted him in a classical manner (although it remained in present tense).
